Well, I don't know if this would be considered a hack, but I was looking through these forums and didn't see anything about reseting the scores in Forza. It was pretty easy to figure out myself, so I just wanted to share with others in case they wanted to do the same...

To reset the scores, delete Leaderboard* in the E:\UDATA\4d53006e\FD69450FB53B\ directory...simple as that.

Thanks I was wondering how to do that because there's this glitch that would sometimes post time of 0:00:00 and it would slowly displace all of my real times.